Rubber anticracking chemicals



Fatented July 29, 1952 UNI-TED SiTAT-E-S PAT fOFFliCiE menses CHEMICALS jfByron*A.f"Hunter,-Oxford, Conn alssignor to United States Ru-bber Company; ;New York mDmwinggApplication January 118; 19 9,

" serial No; .;.71 ,55

":rrms invention relates ito-j ew 'janti cra'cking .f. antioxidants for. naturaland. synthetic jrubbers.

.TOne of themajor rubber ichemical'fprobl'ems'is the protection of rubber"(na1tural andsynthetic) either static or'..,c lynamicstress while subjected'to the influencesof air. .(oxygen; ozone)", heat and/or light (sunlight). I Anobject of this invention to providech'emstantially .obvi'ate i such lir'a'ckiljl'g tendencies. A

further object is to provide a chemical" which,

besides .being.,.a highly .eflective'jjanti=cracking agent; will .be' considerably. less toxic than; other antiecracking agents. ','.Other objects will 'beobviousfrom. the. hereinafter description.

.Such. a. relatively non-toxic 'chernicalis the mono-oxalic acid. salt of N',N:dieseconldarybutyl- V pgpheriylene diamine.

. lThis .Qsais .ufiiquel as less .,.toXic" .thanJlNiN' i-disecondary butyl e, p -,-phe nylene jdia'minei .which (thoughefiectiveasan antiecraekingagent) isso toxic. as .to prohibitiitscommercial use. In spite of :the relative 1-imited1dilution with 1 the oxalic acid, the mono salt retains high effectiveness as.

an'anti-crackingagent. The dioxalic acid salt of N,N'-di-secondary butyl-p-phenylene diamine CH; 4 CH3 is of no value -asianMantiscrackingzichemical.

The following examples ..-of preparation ,and

atestiney are given to illustrate the-invention-pparts are byiweightz (Example 1. Prepaz'd-tio'n.

.. :270 grams 3 moleslof-anhydrous oxalic acid are dissolved in 1500 cc. of ethanol (95%) (with slight warming to hasten solution). Into this solution, with stirring, are poured 666 grams (3 moles) of N,N-di secondary butyl-p-phenylene diamine. The mixture is kept Warm (50 C.) for 30 minutes and is then allowed to stand and cool for about 2 hours. The thick, purple suspension is filtered on a Biichner funnel, spread out on paper sheets and exposed to the air overnight.

Yield 76'7 grams of white crystals (82% of theory). The material melts at 1'70-171 C. The

against cracking .due'to weathering'involving 5 .di-secondary. butyl-prphenylenerdiamin -2. product was analyzedand found to contain 8.77% nitrogen. The calculated value for 9.03 nitrogen. The same-product. camalsebeohtainednsill ,Water rather than alcohol as the reactionmediu n.

In order: to illustrate the-effectiveness enooxalate as ananticra'cking 'chemical-fin rubber rrrhe ingredients were eonibinedionfa ruuhimiu trary scaleofivis'ualcrack ratingibase'd" n numberof similar tests, stocks the following testing data are given:

I. In GR-S (rubbery l,3-butadiene;-styrene .copclymer) jsyntheticrubber compositionswere made. up in accordance: withi'the' 'followingrreclipez StoclcB Mercaptoben zo thiazo ccelejra'tor) N,N-di-secoudary butyl-p -p h e nyl mono-oxalate in the ordinary. way and .jpo'rtionsifiof eac k .were cured, atL45J.poundsjsteamji'efisllre or 90 minutes. '3 Samples, .of the. curedjstonksK 1 .werebent double and" thej eh'ds'. fastened "t Stock A; v Stock B Example 3 In order to demonstrate the effectiveness of N,N'-disecondary butyl-p-phenylene diamine mono-oxalate in retarding outdoor dynamic cracking of GR-S, portions of stocks A and B were cured for minutes (1" x 6" Demattia grooved bending samples) and subjected to re- 3 peated bending on an outdoor bending machine. The samples were exposed to outdoor weathering conditions for 3 months. The machine was operated for approximately 16 hours per day at the rate of 10.5 kilocycles per day. The samples were observed periodically and rated according to an arbitrary visual rating scale based on observations of a large number of similar tests. The data obtained, as shown below, clearly illustrates the superior properties of the new anticracking chemical.

Mercaptobenzothiazole ators, softeners, etc.

Stock A StockB Kilocycles flexing to very, very slight cracks 271. 4, 662

Kilocycles flexing to very slight cracks 456 4, 760

Kilocycles flexing to slight cracks 533 5, 434

Kllocycles flexing to cracks 738 6, 731

II. in natural rubber Easample '4 Natural rubber compounds were made up according to the following recipe:

Stock D Smoked sheets Carbon black Zinc oxide Zinc soap of coconut oil acids Pine tar Sulfur O 2- r s m O OCDIOIQQO N, N -di-secondary butyl-p-phenylene diamine mono-oxalate- .Portions of stocks C and D were cured at 30 pounds steam pressure for 60 minutes and 1" x 4 test pieces were cut. The test pieces were bent double and the ends fastened together and mounted on a board. The samples were then exposed to outdoor weather. 'After 2 days stock C had developed very slight cracks and became badly cracked after 6 days. Stock D, however, showed very slight cracks only after 9 days and became badly cracked only after 14 days.

Example ,,Portions of stocks C and D were cured at 30 C exhibited bad cracks after 233 kilocycles of .fiexing whereas stock D, containing the new anticIacking chemical, showed a similar degree 'of 'compounding ingredients may be incorporated along with the anti-cracking chemical. For example, there may be incorporated other acceler- V pounds steam pressure for minutes (1 x 6 Demattia grooved bending samples) and the re- 'sultingtest pieces were repeatedly flexed on an outdoor bending machine as in Example 3. Stock The anti-cracking chemical may be incorporated in any type of rubber composition, such as those used for automobile tires and tubes, hose, belting, sheet and thread rubber, rubberized fabrics, molded goods, boots and shoes, etc., whether vulcanized in a mold, in open steam, in hot air, or in the cold by the so-called acid process. If the material to which the anti-cracking chemical is added is a liquid such as rubber cement or an oil, it may be dissolved therein in a suitable small proportion. The anti-cracking chemical may be incorporated into solid substances by milling or mastication, and prepared for incorporation in dispersions or solutions either in powder, paste or solution form, or applied in such forms for incorporation by difiusion to the surface of vulcanized or unvulcanized rubber goods.

The term a rubber is employed in the claims to mean a sulfur-vulcanizable plastic material which possesses high extensibility under load, coupled with the property of flexibly retracting to approximately its original size and shape after load is removed, and includes india rubber and other natural rubbers as well as synthetic vulcanizable products such as butadiene polymers, and modified butadiene polymers (Buna N and Buna S, described, respectively, in U. S. Patents Nos. 1,973,000 and 1,938,731) and the like, which have a flexibility and elasticity similar to rubber; and reclaims and latices of such material, whether or not admixed with fillers, pigments, accelerating agents, etc.

Having thus described myinvention, what I claim and desire to protect by Letters Patent is:

l. A rubber composition in which the rubber is from the class consisting of natural rubber, butadiene-styrene copolymer rubber and butadiene-acrylonitrile ccpolymer rubber, containing a mono-oxalic acid salt of N ,N '-di se'condary b'utyl-p-phenylene diamine.

2. A natural rubbercomposition containing a mono-oxalic acid salt of N ,N'-di-secondary butylp-phenylene diamine.

3. A rubbery 1,3butadiene-styrene copolymer composition containinga mono-oxalic acid salt of N,N'-di-secondary butyl-p-phenylene diamine. ,4. A rubbery 1,3-butadiene-acrylonitrile copolymer composition containing a mono-oxalic acid salt of N,N' -di-secondary butyl-p-phenylene diamine.

BYRON A. HUNTER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Gribbins g. 22 1950 

1. A RUBBER COMPOSITION IN WHICH THE RUBBER IS FROM THE CLASS CONSISTING OF NATURAL RUBBER, BUTADIENE-STYRENE COPOLYMER RUBBER AND BUTADIENE-ACRYLONITRILE COPOLYMER RUBBER, CONTAINING A MONO-OXALIC ACID SALT OF N,N''-DI-DI-SECONDARY BUTYL-P-PHENYLENE DIAMINE. 